Material disintegrating apparatus having an adjustable side board



Aprll 26, 1955 G. A. DAILY 2,707,099

MATERIAL DISINTEGRATING APPARATUS HAVING AN ADJUSTABLE SIDE BOARD Filed Dec. 28, 1948 4 Shee-tsSheet l.

llll April 26, 1955 G. A. DAILY 2,707,099

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MATERIAL. DISINTEGRATING APPARATUS' HAVING AN ADJUSTABLE SIDE BOARD Filed Dec. 28, 1948 4 Sheets-Sheet 5 O O O 1:5: h u, E%,U :5 Q m r W. Aw Q00. Mo

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G. A. DAILY MATERIAL DISINTEGRATING APPARATUS HAVING AN ADJUSTABLE SIDE BOARD Filed Dec. 28, 1948 4 Sheets-$heet 4 diioz nqy.

United States Patent MATERIAL DISINTEGRATING APPARATUS HAVING AN ADJUSTABLE SIDE BOARD Glenn A. Daily, Franklin, Pa., assignor to Joy Manufacturing Company, Pittsburgh, Pa., a corporation of Pennsylvania Application December 28, 1948, Serial No. 67,628

6 Claims. (Cl. 262-29) This invention relates to material disintegrating apparatus, and more particularly to such apparatus having im proved means associated with it for preventing the lateral escape from the moving forces provided by the disintegrating devices of the material torn loose by the latter and for thereby insuring the delivery at the rearward end of the disintegrating apparatus of as large an amount of the disintegrated material as possible.

The invention finds particular utility in connection with continuous miners. These are apparatus for the disintegration of mineral veins and the loading out of the disintegrated material, the disintegrating and loading out being carried on as a relatively continuous process. Such apparatus commonly comprises a movable base and mechanism supported by the base for attacking, disintegrating and loading out a series of vertical bands differently transversely disposed across a working face, until a strip extending from the mine floor to the mine roof and for the full width of the working place has been disintegrated and removed, after which another arcuate section extending across the width of the room or entry will be attacked, disintegrated and loaded out. As a consequence of their mode of operation, which consists generally, in the case of the disintegration of any given band, of a sumping in operation, a vertical swinging operation, and, except in special conditions, a withdrawing movement. there will be formed adjacent one ribthe rib at which the disintegration of the first of a series of vertical bands extending across the face is to be effected-a vertical recess extending from mine floor to mine roof and of a depth which has been found most desirable for effecting disintegrating operation and of a width perhaps on the order of two or three feet, which width is determined largely by the power of the machine and by the capacity of the disintegrated material removing equipment. In any event, upon the removal of the first band of material adjacent one rib,

there will be a repositioning of the disintegrating mechanism of the apparatus, a sumping in thereof, usually at the bottom of the next vertical strip to be removed, an upswing thereof, and ordinarily a rectilinear withdrawal thereof. During this process, one side of the disintegrating mechanism will have adjacent to it a vertical wall of coal or other mineral which will prevent the escape of material at that side of the disintegrating mechanism. The other side of the disintegrating mechanism will, however, be, as it were, open, that is. it will be next to an open space formed by the removal of the preceding vertical strip of coal or other mineral. There is thus a serious possibility of substantial escape, laterally of the disintegrating mechanism, of substantial quantities of disintegrated mineral at the latter side of the disintegrating mechanism. This escape of disintegrated material may be considerably reduced if there be provided a side guard plate or side board for obstructing the lateral escape of material. Such a side guard plate or side board will be of maximum effectiveness if it can be extended just as far forwardly of the clistintegrating mechanism as possible, and if it can be maintained in a position such that the upper edge thereof-assuming upward move ment during swing of the disintegrating mechanism will be, during as great a part of the disintegrating cycle as possible, at least as high as the upper run of the disintegrating devices. Moreover, such a device will need to be both retractable longitudinally of the disintegrating mechanism and swingable downwardly, that is, reversely to the direction of upswing of the disintegrating mechanism, in order to take care of interference with its movement by different kinds of obstructions. It will also be desirable to have the side board arrangement so constructed and arranged that if there is interference with its rectilinear forward movement, it may be thrust rearwardly; and if there is interference with its arcuate upward movement, it may be swung downwardly as the disintegrating mechanism continues its upward movement. It is also desirable that such a mechanism be controllable from a point remote from the face, and by 1 power rather than by the force exertable by the runner of the miner.

It is an object of my invention to provide an improved side board arrangement for minimizing the escape from a continuous miner or the like of coal or other disintegrated material as distintegration taken place. It is another object of the invention to provide an improved yslidable and swingable side board type of apparatus for use in association with a disintegrating mechanismone which may be advanced and retracted and. swung upwardly and downwardly and which may include arrangements whereby one of said movements, desirably upswing, may perhaps precede advance. It is a further object of the invention to provide an improved side board arrangement in which the side board may be positionable close to the forward end of the disintegrating apparatus and desirably at least as high as the upper run of the disintegrating elemerits. Still another object of the invention is to provide an improved side board arrangement having an expansible chamber motor controlled positioning mechanism including a slidable and swingable mounting for the side board, and means whereby movement transmitted to the swingable side board may, in a limiting position of the latter, exert a positive force for effecting sliding of the side board, but in which, ordinarily, whether sliding, swinging, or both concurrently shall occur may depend upon the particular conditions encountered. Other objects and advantages of the invention will hereinafter more fully appear.

In the accompanying drawings, in which one illustrative embodiment of the invention is shown,

Fig. l is a plan view of a continuous miner engaged in disintegrating the second of a series of vertical bands extending across the face.

Fig. 2 is a side elevational view of the forward portion of the continuous miner shown in Fig. 1.

Fig. 3 is a top view, with parts broken away, of the disintegrating mechanism shown in Fig. 1.

Fig. 4 is a side elevational view of the disintegrating mechanism shown in Fig. 2, on a larger scale, and with parts broken away, the improved side board arrangement thereof being shown in its forward and raised position.

Fig. 5 is a similar view showing the side board in its forward but lowered position.

Fig. 6 is a similar view showing the side board in its retracted position but with the side board raised.

Fig. 7 is a fragmentary diagrammatic view showing the disintegrating mechanism removing a vertical band at the left-hand rib.

Fig. 8 is a fragmentary diagrammatic view showing the disintegrating mechanism working at the center of a room or entry.

Fig. 9 is a vertical section on the planes of the section line 9-9 of Fig. 6.

Figs. 10 and 11 are diagrammatic views showing fluid supply arrangements.

Referring to the drawings, and initially to Figs. 1 and 2, a continuous miner generally designated 1 is shown in Fig. 1 as operating in an entry 2. It operates by the successive removal of arcuate vertical strips of coal 3 extending for the full width of the entry, and having forward surfaces which form successive faces 4, 4' etc. as advance of the entry takes place. The removal of the successive strips is by the successive removal of a plurality of vertical bands, each extending from the mine floor to the mine roof, of appropriate depth normal to the face and of a width determined by the design of the machine.

The continuous miner includes a portable base 5 which may be of any suitable construction, but which is desirably tractor-mounted and propelled. On this base there is arranged a turntable mechanism 6, relative to which there is reciprocable a slidable frame 8 which is oppositely movable to effect sumping and withdrawing movements of a disintegrating mechanism driven by a motor 9 and itself designated 10. The disintegrating mechanism includes a vertically swingable frame 11 pivoted for vertical movement about an axis 12 and adapted to be swung vertically by hydraulic cylinder and piston means 13 connected by a connecting rod 14 to a depending arm 15 carried by the disintegrating mechanism. The disintegrating mechanism provides appropriate guides for a series of circulating chains, a portion of these guides being shown in Fig. 3 in which they are designated 16, 17, 18, 19 and 20. Guides at the opposite sides of the paths of the circulating chains mentioned cooperate in guiding the latter. A series of four circulating chains, designated 21, 22, 23 and 24, is shown in the drawings, but it will be appreciated that the invention is not limited to any particular number of chains or, necessarily, even to chains at all. The circulating chains include disintegrating element-carrying blocks 25 connected by intermediate links 26. Disintegrating elements 27 are carried by the blocks 25, and these are illustrated as in the general form of conventional cutter bits, but they may obviously assume various forms and they may also be arranged in various patterns by the appropriate arrangement of the several chains with respect to each other. The particular pattern of the disintegrating elements is that which is illustrated in the application of Harold F. Silver, Serial No. 11,688, filed February 27, 1948, which application is owned by my assignee.

The disintegrating apparatus has as a part of it side walls 30 forming, at their upper portions, a trough which guides the disintegrated material and prevents the lateral escape thereof as the upper runs of the chains 21, 22, 23 and 24 carry the material back toward an opening 31 to a hopper from which the material is moved by suitable conveying means to a rearward point of discharge. These fixed side walls are tapered at their forward ends as shown at 32 so as not to strike the roof in the raised positions of the disintegrating mechanism. Necessarily, since they are not adjustable relative to the disintegrating mechanism, they must terminate at a point at least slightly more remote from the innermost (forward) end of the disintegrating mechanism than the maximum depth of penetration of the disintegrating mechanism. Thus there will be a substantial distance forwardly of the side walls 30 along which lateral escape of material is possible if no other provision is made. This distance at the side of the disintegrating mechanism which is not closed by the side wall 30 to the escape of undisintegrated material may be on the order of close to two feet in length and the space may be several inches in height. During the upswing, disintegrating of material will be taking place from a position about opposite the vertical center of the forwardmost point of the disintegrating mechanism upwardly and outwardly to the point where the disintegrating elements emerge from the face.

To prevent as completely as possible the escape of material, I have provided in the illustrative embodiment of my invention a slidable and swingable side board arrangement which I shall now describe. First, however, it may be well to note that the side walls 30 of the frame which guides the chains carrying the disintegrating elements are relatively upright, and that at their tops they comprise trough-forrning elements 36 consisting of outwardly sloping portions 37 and upper vertical portions 38, the latter being spaced apart from each other more widely than the lower portions of the side walls 30.

A box-shaped guide structure 40 is suitably secured, as by welding, to one of the side plates 30 and extends longitudinally of the latter, and has an upper. angle portion 41 having a downwardly turned flange 42 and a lower guide element 43 having an upwardly turned flange 44, these forming a guideway 45 in which a shoe 46 is slidable longitudinally of the disintegrating mechanism, the direction of sliding being substantially longitudinally of the disintegrating mechanism and the guideway being arranged near the upper part of the side plates 30. A stop S closes the forward end of the guideway 45 and limits the forward movement of the shoe 46. The shoe 46 carries a forwardly and upwardly projecting arm 47 which rotatably supports a pivot pin 48 secured to the upper rearward corner of a side board 49. The side board 49 as illustrated is elongated and has parallel upper and lower sides 50, 51, a generally rounded forward end 52,

of which the downward forward curvature extends well below the longitudinal center and its rearward end is cut away obliquely at 53. Near the junction of the lower side 51 and the oblique rearward end 53, there is supported by the sideboard another pin 54, which extends through a bearing 55 provided at the forward end of a piston rod 56. The piston rod 56 carries a piston 57 which is reciprocable in a cylinder 58 pivotally supported at 59 on a pin 60 extending outwardly from the side wall 30. Hydraulic fluid may be admitted under the control of any suitable valve mechanism, not shown, and through connections 61 and 62 to the opposite ends of the cylinder 58 and effect retraction of the piston 57 or forward movement thereof. Spray water for the disintegrating mechanism, at a pressure on the order of p. s. i. is a satisfactory source of hydraulic fluid for the cylinder and piston mechanism, and such a pressure allows the forces which may be encountered in the use of the device to overcome the hydraulically produced forces. Because any ordinary four-way valve will suflice for the supply of fluid to the connections 61, 62 and for the venting of fluid therefrom, the control for the supply and venting of fluid from these conduits is not shown in the drawings.

When spray water is the source of the supply to the connections 61 and 62, as per Fig. 10, the open spray nozzles provide a relief for the fluid displaced in the event the piston 57 is forced backwardly in the cylinder 58. A usual relief valve in the discharge line from a pump could serve the same function, as indicated in Fig. 11. It will be clear that, if desired, pressure could be applied continuously to the connection 62 whenever the apparatus was in use, in which event the device would be in effectand could actually be constructed as-a single acting jack.

The pivotal mounting at 59 and the pivotal connection at 54 with the piston rod 56 permit the cylinder 58 to adjust itself to the different angular positions occasioned by the swing of the side board 49 about the pivot 48 and the changes in the longitudinal position of the side heard through sliding of the bracket 47 and the guide or shoe 46 in the guide arrangement 40. The arm or bracket 47 carries a stop 63, and the side board 49 a stop 64 adapted to cooperate with the stop 63, to prevent upward swinging of the side board beyond a position in which its upper and lower edges will be parallel to the longitudinal center line of the disintegrating mechanism.

The mode of operation of the arrangement described may be readily understood by observing Figs. 2, 4, 5 and 6. Fig. 6 shows the side board 49 in its retracted raised position, a position it is likely to assume ordinarily only when the side board is pushed back as a result of sumping straight in.

In the fully retracted position of the side board, the slide 46 is likely to be in a position intermediate between the ones shown in Figs. 5 and 6, and the side board 49 is likely to be in the approximate angular position shown in Fig. 5. Then, when fluid is supplied to the rear end of the cylinder 58 through the connection 62, whether the side board will move up to the horizontal position shown in Fig. 6, or whether it will remain in its lowered position shown in Fig. 5 while the slide 46 moves forwardly until it engages the stop S, or whether there will be a concurrent dual motion, consisting in part of bodily advance and part of upswing, will depend entirely on the resistances to movement which happen to exist at the time. The side board will, however, attain to the position shown in Fig. 4, unless there is an obstruction to its movement.

It could be moved from the position shown in Fig. 4.

down to the position shown in Fig. Sif there were an obstruction to upward movement of the side board met during upswing of the disintegrating apparatus. It could be moved all the way back to the position shown in Fig. 6 if, for any reason, there were rectilinear sumping of the disintegrating apparatus in a substantially horizontal position and an obstruction was met. It will be appreciated that the side board may assume a wide variety of positions, depending upon the point where obstruction is encountered and the direction of movement of the side board with, or relative to, the disintegrating apparatus when the obstruction is encountered. In the extreme topmost position of the disintegrating apparatus, the side board will have its outer forward end depressed, at least so that it will not prolest above the highest point in the orbit of the disintegrating devices, unless these cut away more coal in the previous vertical swing than they remove during the one in process. It will be understood that the side board may encounter obstruction to its movement from cores or projecting ribs of coal, as, for example, if the successive disintegrating cycles do not overlap each other completely. In case a heavy lump of coal were to fall on the outer end of the side board it might be depressed. Other conceivable circumstances will suggest themselves to those skilled in the art which might occasion the outward forcing or the downward swinging of the side board. It will be appreciated from what has been said that this improved side board arrangement will very effectively prevent the lateral escape at least of large amounts of disintegrated material toward the otherwise free side of the disintegrating apparatus, because it extends so far forwardly-substantially as far forward as the forward end of the guide frame of the disintegrating chains, and that, because there is clearance above it, since it is moving at the open or free side of the band of material being attacked, it may actually extend above the tops of the disintegrating elements as they move rectilinearly outwardly, at least until nearly the top of the upswing of the disintegrating mechanism. In the event that during upswing or even before upswing commences there is any obstruction to the free movement-4n whatever direc tion that is taking place-of the side board 49, this element may either cease its movement or indeed be moved rearwardly and/or downwardly with respect to the remainder of the disintegrating mechanism per se. Thus it will be appreciated that not only is there a very effective means provided for preventing the lateral escape of material, but also means is provided for this purpose which is thoroughly protected against breakage.

While there is in this application specifically described one form which the invention may assume in practice, it will be understood that this form of the same is shown for purposes of illustration and that the invention may be modified and embodied in various other forms without departing from its spirit or the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent is:

1. In a disintegrating and material-conveying mechanism, a bar structure having extending along its op posite sides upwardly projecting walls cooperating with said bar structure to form an open-topped trough, said upwardly projecting walls terminating short of the forward end of said bar structure, disintegrating elements carried by said bar structure and supported for movements in parallel orbits in upright planes extending between said upwardly projecting walls, said orbits having forward portions at the forward end of said bar structure in advance of the forward ends of said upwardly projecting walls, an element mounted on said bar structure and movable relative to the latter in upright planes between positions in one of which it forms an extension of the upwardly projecting wall at its side of said bar structure which lies alongside, but outwardly of, the most. adjacent orbit, at a portion of the latter in which, during a vein-attacking operation, the disintegrating elements thereof engage material to be disintegrated and in another of which said element extends downwardly transversely with respect to the side of said bar structure and wholly to the rear of the portion of said most adjacent orbit in which the dlsintegrating elements engage material to be disintegrated, and means for supporting said element in said positions and moving it between them including a guideway mounted on one side of said bar structure and extend ing lengthwise thereof, a slide reciprocably mounted on said guideway, a pivotal mounting for said element on said slide on which pivotal mounting said element is swingable on a horizontal axis transverse to said bar structure between positions in which it extends forwardly lengthwise of said bar structure and in which it extends downwardly transversely of said bar structure, and an expansible jack comprising a jack element pivotally connected to said bar structure and a relatively longitudinally movable jack element pivotally connected to said first mentioned element at a point at all times below said horizontal axis in a horizontal position of said bar structure.

2. In a disintegrating and material-conveying mechanism, a bar structure having extending along its opposite sides upwardly projecting walls cooperating with said bar structure to form an open-topped trough, said upwardly projecting walls terminating short of the forward end of said bar structure, disintegrating elements carried by said bar structure and supported for movements in parallel orbits in upright planes extending between said upwardly projecting walls, said orbits having for ward portions at the forward end of said bar structure in advance of the forward ends of said upwardly projecting walls, an element mounted on said bar structure and movable relative to the latter in upright planes between positions in one of which it forms an extension of the upwardly projecting wall at its side of said bar structure which lies alongside, but outwardly of, the most adjacent orbit, at a portion of the latter in which, during a vein-attacking operation, the disintegrating elements thereof engage material to be disintegrated and in another of which said element extends downwardly transversely with respect to the side of said bar structure and wholly to the rear of the portion of said most adjacent orbit in which the disintegrating elements engage material to be disintegrated, and means for supporting said element in said positions and moving it between them including a guideway mounted on one side of said bar structure and extending lengthwise thereof, a slide reciprocably mounted on said guideway, a stop for limiting the forward movement of said slide on said guideway, a pivotal mounting for said element on said slide on which pivotal mounting said element is swingable on a horizontal axis transverse to said bar structure between positions in which it extends forwardly lengthwise of said bar structure and in which it extends downwardly transversely of said bar structure, and an expansible jack comprising a jack element pivotally connected to said bar structure and a relatively longtiudinal movable jack element pivotally connected to said first mentioned element, said stop positioned to limit forward movement of said slide on said guideway to a distance less than the length of relative movement of said jack elements.

3. In a disintegrating and material-conveying mechanism, a bar structure having extending along its opposite sides upwardly projecting walls cooperating with said bar structure to form an open-topped trough, said upwardly projecting walls terminating short of the forward end of said bar structure, disintegrating elements carried by said bar structure and supported for movements in parallel orbits in upright planes extending between said upwardly projecting walls, said orbits having forward portions at the forward end of said bar structure in advance of the forward ends of said upwardly projecting walls, an element mounted on said bar structure and movable relative to the latter in upright planes between positions in one of which it forms an extension of the upwardly projecting wall at its side of said bar structure which lies alongside, but outwardly of, the most adjacent orbit, at a portion of the latter in which, during a vein-attacking operation, the disintegrating elements thereof engage material to be disintegrated and in another of which said element extends downwardly transversely with respect to the side of said bar structure and wholly to the rear of the portion of said most adja cent orbit in which the disintegrating elements engage material to be disintegrated, and means for supporting said element in said positions and moving it between them including a guideway mounted on one side of said bar structure and extending lengthwise thereof, a slide reciprocably mounted on said guideway, a pivotal mounting for said element on said slide on which pivotal mounting said element is swingable on a horizontal axis transverse to said bar structure between positions in which it extends forwardly lengthwise of said bar structure and in which it extends downwardly transversely of said bar structure, a stop for limiting upward swinging of said element relative to said slide and an expansible jack comprising a jack element pivotally connected to said bar structure and a relatively longitudinally movable jack element pivotally connected to said first mentioned element at a point thereon lower than said pivotal mounting.

4. In a disintegrating and material-conveying mechanism, a bar structure having extending along its opposite sides upwardly projecting walls cooperating with said bar structure to form an open-topped trough, said upwardly projecting walls terminating short of the forward end of said bar structure, disintegrating elements carried by said bar structure and supported for movements in parallel orbits in upright planes extending between said upwardly projecting walls, said orbits having forward portions at the forward end of said bar structure in advance of the forward ends of said upwardly projecting walls, an element mounted on said bar structure and movable relative to the latter in'upright planes between positions in one of which it forms an extension of the upwardly projecting wall at its side of said bar structure which lies alongside, but outwardly of, the most adjacent orbit, at a portion of the latter in which, during a veinattacking operation, the disintegrating elements thereof engage material to be disintegrated and in another of which said element extends downwardly transversely with respect to the side of said bar structure and wholly to the rear of the portion of said most adjacent orbit in which the disintegrating elements engage material to be disintegrated, and means for supporting said element in said positions and moving it between them including a guideway mounted on one side of said bar structure and extending lengthwise thereof, a slide reciprocably mounted on said guideway, a pivotal mounting for said element, adjacent the upper rearward portion thereof when the same is longitudinally extending, on said slide on which pivotal mounting said element is swingable on a horizontal axis transverse to said bar structure between positions in which it extends forwardly lengthwise of said bar structure and in which it extends downwardly transversely of said bar structure, and an expansible jack comprising a jack element pivotally connected to said bar structure and a relatively longitudinally movable jack element pivotally connected to said first mentioned element at a point at all times below said horizontal axis in a horizontal position of said bar structure.

5. In a disintegrating and material-conveying mechanism, a bar structure having extending along its opposite sides upwardly projecting walls cooperating with said bar structure to form an open-topped trough, said upwardly projecting walls terminating short of the forward end of said bar structure, disintegrating elements carried by said bar structure and supported for movements in parallel orbits in upright planes extending between said upwardly projecting walls, said orbits having forward portions at the forward end of said bar structure in advance of the forward ends of said upwardly projecting walls, an element mounted on said bar structure and movable relative to the latter in upright planes between positions in one of which it forms an extension of the upwardly projecting wall at its side of said bar structure which lies alongside, but outwardly of, the most adjacent orbit, at a portion of the latter in which, during a veinattacking operation, the disintegrating elements thereof engage material to be disintegrated and in another of which said element extends downwardly transversely with respect to the side of said bar structure and wholly to the rear of the portion of said most adjacent orbit in which the disintegrating elements engage material to be disintegrated, and means for supporting said element in said positions and moving it between them including a guideway mounted on one side of said bar structure and extending lengthwise thereof, a slide reciprocably mounted on said guideway, a pivotal mounting for said element on said slide on which pivotal mounting said element is swingable on a horizontal axis transverse to said bar structure between positions in which it extends forwardly lengthwise of said bar structure and in which it extends downwardly transversely of said bar structure, and an expansible jack comprising a jack element pivotally con-- nected to said bar structure and a relatively longitudinally movable jack element pivotally connected to said first mentioned element at a point at all times below said horizontal axis in a horizontal position of said bar structure, said slide having a raised, forwardly extending portion on which said pivotal mounting is supported, and said first mentioned element having its connection with said pivotal mounting at its upper rearward portion when it is horizontally disposed.

6. In a disintegrating and material-conveying mechanism, a bar structure having extending along its opposite sides upwardly projecting walls cooperating with said bar structure to form an open-topped trough, said upwardly projecting walls terminating short of the forward end of said bar structure, disintegrating elements carried by said bar structure and supported for movements in parallel orbits in upright planes extending between said upwardly projecting walls, said orbits having forward portions at the forward end of said bar structure in advance of the forward ends of said upwardly projecting walls, an element mounted on said bar structure and movable relative to the latter in upright planes between positions in one of which it forms an extension of the upwardly projecting wall at its side of said bar structure which lies alongside, but outwardly of, the most adacent orbit, at a portion of the latter in which, during a vein-attacking operation, the disintegrating elements thereof engage material to be disintegrated and in another of which said element extends downwardly transversely with respect to the side of said bar structure and wholly to the rear of the portion of said most adjacent orbit in wh ch the disintegrating elements engage material to be disintegrated, and means for supporting said element in said positions and moving it between them including a guideway mounted on one side of said bar structure and extendmg lengthwise thereof, a slide reciprocably mounted on said guideway, a pivotal mounting for said element on said slide on which pivotal mounting said element is swingable on a horizontal axis transverse to said bar structure between positions in which it extends forwardly lengthwise of said bar structure and in which it extends downwardly transversely of said bar structure, and an expansible jack comprising a jack element pivotally connected to said bar structure and a relatively longltudinally movable jack element pivotally connected to said first mentioned element, said last mentioned pivotal connection at a point on said first mentioned element which 15 respectively forward of and rearward of said pivotal mounting, and in each case below the same, in the first and second mentioned positions of said first mentioned element.

References Cited in the file of this patent UNITED STATES PATENTS 1,549,699 Wilson Aug. 11, 1925 1,864,785 Wilhelmi June 28, 1932 1,998,529 Vander Hulst Apr. 23, 1935 2,422,985 Reckler June 24, 1947 2,441,581 McDade May 18, 1948 

